With that mentioned the part looks to be no longer available so you may have to start calling some Merc dealers to see if they have an old throttle body in the junk pile or ask them to run the part number to see if any other merc dealer has one listed in old stock.
Image search the part number for a visual....Hope this helps some, good luck.
If your unable to find it, and your kind of handy you might be able to make one out of aluminum bar stock. Had a plastic part break on my throttle body (different then yours) and had it made at a machine shop
